The ability of two-dimensional polyacrylamide gel electrophoresis to resolve complex mixtures of proteins, including total cell protein, has become a powerful tool in cell biology. It is uniquely useful in revealing effects of environmental, nutritional, and pathological conditions on the synthesis, degradation and post- translational modification of individual cellular proteins because it provides an image of the global response of the cell or organism, permitting hitherto unidentified proteins to be recognized as participants in a response. Use of two-dimensional gels has already contributed much new information about patterns of regulation of gene expression. The construction of inventories of the resolved proteins of some intensively studied cells (e.g., Escherichia coli and human lymphocytes) will increase further the value of two-dimensional gels in many aspects of biomedical science. This usefulness in illustrated by the variety of research projects being conducted by members of the core users group described in this application: The cellular heat-shock response will be examined in Escherichia coli and selected eucaryotic cells in a study designed to analyze the components of the response, their biological function, and the mechanism of the response (Neidhardt). The participation of phage and bacteria cell components is regulating the termination of transcription will be studied through the use of phage and cell mutants (Friedman). Changes in the expression of plasmid-encoded virulence genes of Salmonella typhimurium will be studied during the transition from laboratory media to growth in human host tissue (Jones). Cultured islet cells of the rat pancreas will be analyzed to detect proteins uniquely associated with hormone production (Pek). The role of phosphorylation in the regulation of glucocorticoid receptors from mouse L-cells, and the possible identity of this receptor to a glucose-regulated heat-shock protein will be investigated (Pratt). The pattern of phosphorylation of proteins in rat testis Sertoli cells in response to hormones and to interaction of these cell with germ cells will be examined. Preparations of mitotic spindles of cultured with germ cells will be examined to identify calmodulin-binding proteins (Welsh). Each of these projects requires quantitative and qualitative analysis of images of two-dimensional protein gels.